Body mass index is weight divided by height squared - a rough screening number, not a diagnosis. Enter your height and weight in either metric or imperial units to see your BMI, the category it falls in, and what weight range would put you in the 18.5 to 25 band.
BMI is weight in kilograms divided by height in metres squared. It was devised in the 1830s by Adolphe Quetelet to describe populations, not to assess individuals, and that origin still shows. As a cheap screening signal across large groups it works well. As a verdict on one person it is crude.
BMI cannot tell muscle from fat, so athletes routinely register as overweight. It ignores where fat sits, though abdominal fat carries far more metabolic risk than fat elsewhere. It scales with the square of height when human bodies scale closer to a power of 2.3, so it reads high for tall people and low for short ones. Waist-to-height ratio - keeping your waist under half your height - is a better single number for most people.
Cardiometabolic risk rises at a lower BMI in many South and East Asian populations, and several health authorities use 23 rather than 25 as the overweight threshold for those groups. The categories shown here are the standard WHO adult thresholds. They do not apply to children, who are assessed on age-and-sex percentiles, or to pregnancy.
Below 18.5 is underweight, 18.5 to 24.9 is the healthy range, 25 to 29.9 is overweight and 30 or above is obese. These thresholds are for adults; children are assessed against age and sex percentiles instead.
As a population screening tool it is useful. For an individual it can mislead badly, because it cannot distinguish muscle from fat or account for frame size and fat distribution. Muscular athletes routinely score as overweight. Waist circumference and body fat percentage add information BMI misses.
No. Health risk starts to rise at a lower BMI in some South and East Asian populations, and several health bodies use a lower overweight threshold of 23 for those groups. BMI is a starting point for a conversation with a clinician, not a verdict.
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